The present invention relates, in general, to the field of thin-film data transducers for magnetic storage media. More particularly, the present invention relates to a data transducer and method for writing data to a magnetic storage media, such as DLT computer tape (DLT.TM. is a trademark of Quantum Corporation, Milpitas, Calif.), utilizing the bottom (or lower) pole as the trailing edge of a write head.
Magnetoresistive ("MR") heads for disk and tape media comprise separate read and write head elements formed over each other and generally sharing certain common material layers. The read element usually consists of an alloy film such as nickel-iron ("NiFe") that exhibits a change in resistance in the presence of a magnetic field. Shielding layers protect the MR elements from other magnetic fields, such as those from the associated write head.
The write head element of an MR transducer is designed much the same way as a thin-film inductive head. It generally comprises two magnetic-pole pieces that are typically made of permalloy, a soft magnetic material. These pole pieces are connected at the ends opposite the media and a deposited-layer copper coil is formed therebetween. When an electrical current is supplied to the coil, it produces a magnetic field across the gap between the two inner ends of the pole pieces at the surface of the head adjacent the media. The magnetic fringe field associated with that gap is used to write data onto a magnetic storage media (disk or tape) by reversing the direction of the magnetic fields on the media surface. The number of turns in the write head coil may be as few as ten or less and the lower inductance this affords over the greater number of turns required in conventional thin-film heads makes it easier to write the signal to the media at very high data frequencies.
DLT technology, as opposed to alternative helical scan technologies, segments a tape media into parallel, horizontal tracks and records data by moving the tape past a stationary head at between 100-300 inches per second during read/write accesses and faster during search operations. This longitudinal recording approach allows for the addition of multiple read and write elements to the head to significantly increase data transfer rates. Current DLT products can read or write two or even four channels simultaneously using multiple read/write elements in the head effectively doubling or quadrupling the transfer rate possible at a given drive speed and recording density. Also, DLT products available from Quantum Corporation, Milpitas, Calif., assignee of the present invention, utilize a linear, serpentine recording approach which allows the drive to read multiple data channels simultaneously. The innovative symmetric phase recording ("SPR") technique also developed by Quantum Corporation enhances conventional DLT recording techniques by writing adjacent tracks with an alternating head angle to eliminate cross-track interference and the need for guard bands making smaller track pitch possible.
Conventionally, thin film heads for both disk and tape media have traditionally had the width of the top pole narrower than the width of the bottom pole in order to assure a straight gap line during fabrication. This results, however, in magnetic field contours which are curved outward around the edges of the narrower top pole. Since writing, or encoding, of data occurs as the media moves past the region of the trailing edge pole, and since disk heads use the substrate as the slider body, (which necessitates that the top pole ("P2") be the trailing edge pole), the written transitions are curved at the track edges. However, since tape heads do not require the substrate to serve as a slider body because there is a cap attached to the write head, the present invention advantageously provides that tape heads be constructed and utilized such that the relatively wider bottom pole forms the trailing edge pole of the write head. This serves to decrease the curved transitions at the track edges.
This use of the bottom pole as the trailing edge pole of the write head is especially helpful in applications utilizing certain advanced materials such as FeN-based alloys that have lower permeability when sputtered on sloped surfaces, such as the ramped ends of the top pole as it passes over the underlying write coil. In addition, this can be helpful in patterning sputtered materials such as CoZrTa, since the magnetic track width can be defined by the top pole and the edges of the bottom pole are not critical dimensions and can be wet-etched without loss of track-width control.
As previously noted, in a conventional thin-film data transducer, the bottom pole is typically wider than the top pole so that the edges of the top pole do not overlap the edges of the bottom pole. While the top pole may be fabricated to be wider than the bottom pole at the media-facing surface through additional complicated processing steps, it cannot be made substantially planar due to the fact that it still must be fabricated overlying the write head coil.
Write operations occur at the trailing edge pole of the write head because the field generated by the head in front of the write gap can change the direction of the magnetization of the media when the media is in front of the gap. Resultantly, there exists a region in front of the gap where the field generated by the head exceeds the coercivity of the media. This is commonly referred to as the "write-bubble". If the direction of the field generated by the head changes, it will change the direction of magnetization of the section of the media that is inside this write-bubble. As the magnetic media moves away from the gap, it is no longer influenced by the field generated there, so the direction of magnetization in the media will remain the same as it is when it leaves the write bubble. Therefore, the shape of the field contour and the field gradient are most critical over the tailing edge pole since that is where the magnetization in the media is set.